The present invention pertains to the pressure transducer art and, more particularly, to a means for producing an activated electrical switching state in response to a predetermined fluid pressure level.
Numerous pressure transducer switching systems are known to the prior art. Such systems commonly employ a piston which is caused to displace as a function of applied fluid pressure. A spring system force bias on the piston resists fluid pressure displacement such that piston movement occurs only for applied fluid pressures above a predetermined level and through a predetermined range to a travel limiting stop.
Commonly, mechanical switch contacts are positioned to be activated by the piston in its displaced state. Such mechanical contact type switching systems have suffered from several disadvantages. The switch contacts have been known to chatter under vibration, and are susceptible to corrosion and wear. In addition, inasmuch as the mechanical contacts require moving elements, the repeatability of activation of the switch at a given displacement of the piston has been, for certain applications, unacceptable. Also, over-center snap action electrical switches, normally used to improve switch contact reliability and life, add to the hysteresis, or "dead-band," between switch "open" and "closed" pressure levels.
Attempts have been made at eliminating the mechanical switching contacts by the use of a proximity switch, such as of the magnetic type. Thus, for example, a magnetically responding switch may be positioned at a predetermined position with respect to the travel of the piston such that a magnet, or magnetic material on the piston activates the switch. Whereas the use of such proximity switches has eliminated the problems due to mechanical switch contact wear and wide "dead-band," none of the pressure transducer type switches known in the prior art have provided a means to compensate for the effects of wear in the spring system. Typically, as the spring system and contacting bearing members wear, a given amount of fluid pressure creates a greater total displacement of the piston. Thus, a system originally designed to switch at a given pressure and a specific physical displacement will, with wear of the spring and bearing contact areas, begin switching at a lesser pressure. Without a means to compensate for spring system wear, such prior art systems have required recalibration, or replacement in applications wherein switch activation at a predetermined fluid pressure is critical.